1. Field of the Invention
The present invention finds particular application in papermaker's felts which are employed in the press section of a papermaking machine. As will be known to those skilled in the art, papermaking machines generally include three sections which are generally referred to as the formation, press and dryer sections.
A felt is generally employed to transport the formed, wet sheet through the press and dryer sections of the papermaking equipment. The felt must be particularly adapted to specific conditions encountered in papermaking.
Typically, such felts include a supporting base, such as a fabric woven from yarns or formed from spirals, and a paper carrying or supporting layer fixed to the base. Generally, the paper carrying or supporting layer is softer and smoother than the base layer. Frequently, the base fabric is encased in felt material and felt layers will form both the paper carrying surface and the machine contact surface of the felt.
Slight irregularities or imperfection in the support layer are undesirable in virtually all papermaking operations. Inconsistencies in the felt thickness, gauge or weight can cause undesirable characteristics in the paper or undesirable vibrations during operation of the equipment. Typically, the support layer is a non-woven batt material which has been affixed to the base and has homogeneous characteristics as to permeability, compaction and drainage.
Typically, a papermaker's felt will employ a base fabric which is woven and used as an endless loop. In such an endless felt, there is generally no seam. Although there are some endless woven felt designs which incorporate a seam, seams are generally employed for closing a flat woven fabric into an endless loop. The seam may be of the pin type which utilizes an on machine closure device to complete the loop or of the woven type in which the seam area is back woven to form an endless loop.
The present invention is primarily concerned with papermaker's fabrics which are woven and then formed into an endless loop through the use of a joining wire or pintle. These seams are generally called "pin-seams". As will be recognized by those skilled in the art, it is essential that the seam area be substantially consistent in characteristics with the rest of the fabric. Variations in fabric quality at the seam and/or variations in the seam air permeability, compaction or drainage characteristics may adversely affect the felt life or product quality.
Installation of the seamed felts is generally accomplished by slitting the felt in the area of the seam and removing the pintle. Once the fabric has been installed on the equipment, the pintle is reinserted to close the fabric seam. As a result of cutting or slitting the felt, various difficulties have been experienced with the reliability of the seam. Accordingly, the art has sought to achieve a seamed felt in which the characteristics of the seam area were substantially the same as those of the remainder of the felt.
2. Description of the Prior Art
U.S. Pat. No. 4,601,785 discloses a seamed felt in which the batt layer is cut at a predetermined distance away from the seam and freed from the base, thereby creating a flap. The flap of batt material is intended to overlie over the seam after the fabric ends are joined together. In this approach to seaming a felt, the seaming joint and the abutting ends of the batt material splice lie in different parallel vertical planes.
U.S. Pat. No. 4,279,676 discloses a multi-ply felt formed into an endless loop by a spl,,icing method in which the ends of the multiple plies are offset and used to protect the seam by being formed into flaps which overlie the seam after closure thereof.
Papermaker's felts having a flap over the seam area have been found acceptable in some applications. However, formation of the flap on the felt during seaming can be both cumbersome a nd can result in undesirable operating characteristics. Problems of bounce, excessive felt wear and poor product quality have been associated with flaps which performed less than perfectly. Also, if the flap is not properly resecured after closing of the seam, marking of the end product and adverse wear to the felt and equipment can be caused by the unsecured flap. Experience has shown that the area of the felt adjacent the flap area frequently has different air permeability and water drainage characteristics and may have a different caliper than the remainder of the fabric.
The present invention seeks to address the prior art problems with a solution that is relatively simple and easily implemented.